1. Field of the Invention
The present invention relates to a printer with a memory for storing bit image data, particularly, a printer which prints data fed from a data processing unit such as a host computer or the like and a printing method thereof.
2. Related Art
Conventionally, two printing methods has been applied to a printer having a memory for storing bit image data: a full bit map method whereby data of one page to be printed are written in a bit map memory having a one-page storage capacity, and a strip map method whereby two bit map memories, called as band buffers into which a portion of one-page data is able to be stored, are alternately used to write and read the data portions.
According to the former full bit map method, an image written in the bit map memory can be printed without further processing, so that the processing of data is simple and printing is carried out at high speeds. In contrast, the latter strip map method needs more complicated processing. It takes a considerable time to analyze particularly vector graphic data, from the receipt of data to the start of printing thereof. As a result, the printing speed according to the strip map method may be decreased as a whole. Moreover, in the case of a page printer, e.g., a laser printer, it may happen that the bit-mapping (writing) of data in the memory is unable to catch up with the printing speed, thereby causing such a trouble as missing of an image.
In the meantime, it has been developed in recent years to add an optional memory to a printer so that the strip map method can be changed to the full bit map method, with an aim to improve the printing efficiency.
Even in the case where the full bit map method is applicable to a printer, if the storage capacity of the memory is limited, the full bit map method is effective only for processing the data of a predetermined image size, and should be switched to the strip map method for the data having a size exceeding the predetermined image size.
For example, if the full bit map method is used for an image of A4 size (wherein the actual image area is 7.times.10 inches) with the resolution of 300 dots per inch in longitudinal and lateral directions, the capacity of the memory of (7.times.300).times.(10.times.300).div.8.div.1024.perspectiveto.0.77M bytes is needed. Therefore, if the printer has a memory of 0.5M byte capacity, the full bit map method is useful only for half a page (namely, A5 image size, 7.times.5 inches), and an optional memory of 0.3M byte capacity should be added. When the capacity is 0.8M bytes in total, the full bit map method can be used for A4 size.
However, if the same printer is used, the full bit map method is not applicable to printing of B4 image size due to deficiency of memory capacity. Although it is possible in theory to use the full bit map method to any size of image if the memory capacity is increased without limit by disregarding the limit of hardware of the printer such as a paper feed system or the like, it is not practically available owing to the cost for providing a memory having an unnecessarily large capacity in order to adopt the full bit map method. Furthermore, even if the memory capacity is increased, control such as the management of address becomes inevitably complicated.
Therefore, addition of a memory cannot be said as a fundamental solution of improving the printing efficiency, and it is required for practical purposes that the full bit map method can be switched to the strip map method.
Conventionally, in a printer wherein the full bit map mode and the strip map mode are provided, the full bit map mode can be switched to the strip map mode through manual setting of the printer before the printer is started. Accordingly, once the full bit map mode is set for the printer, all the data to be printed cannot be printed if the amount of the data exceeds the capacity of the bit map memory, and only the data stored in the memory can be printed. On the contrary, once the strip map mode is set, even if all the data to be printed can be accommodated in the bit map memory or the full bit map method is utilizable, printing is executed by the strip map method, thereby lowering the printing speed and printing efficiency, or generating missing of a portion of the image.